1. Field of the Invention
This invention relates to a spinneret device for conjugate melt-blow spinning. More particularly it relates to a spinneret device for side-be-side type conjugate melt-blow spinning wherein two kinds of spinning dopes are melt-extruded from spinning nozzles to form side-by-side conjugate fibers, followed by blow-spinning the extruded unstretched fibers by means of a high speed gas current. Microfine fibers obtained by means of such a spinning device are processed into a web-form product, a non-woven fabric or a molded product and used for a mask, a filter for precision filtration, a battery separator, a hygienic material, a thermal insulant, etc.
2. Description of the Prior Art
The so-called melt-blow spinning wherein a thermoplastic synthetic resin is melt-extruded from spinning nozzles followed by spouting a high temperature gas at a high speed from clearances provided on both sides of the spinning nozzles onto the extruded unstretched fibers to effect blow-spinning, makes it possible to obtain microfine fibers such as those having a fiber diameter of 10 .mu.m or less. Since spinning of fibers and production of a non-woven fabric are carried out successively, the above process is advantageous for producing a non-woven fabric of microfine fibers.
There are two ways for melt-blow spinning, one of which is by means of non-conjugate fibers and the other is by means of conjugate fibers.
As to the melt-blow spinning of non-conjugate fibers, a device and spinning process are disclosed in Industrial and Engineering Chemistry, Vol. 48, No. 8, pp 1342-1346, 1956. Japanese patent application laid-open No. Sho 50-46972 and Japanese patent application laid-open No. Sho 54-134177 disclose a process wherein spinning is carried out while decomposing a polymer or while keeping the spinning conditions such as the apparent viscosity, extrusion temperature, etc. of a polymer within specified critical ranges, along with an apparatus therefor. However, the above-mentioned references do not disclose any spinning of conjugate fibers.
As to the so-called conjugate melt-blow spinning directed to conjugate fibers, Japanese patent application laid-open No. Sho 60-99057 and Japanese patent application laid-open No. Sho 60-99058 disclose a spinneret device for side-by-side conjugate melt-blow spinning, provided with conduits for introducing two kinds of polymers from the respective extruders therefor, into holes for combining conjugate components of the polymers, spinning nozzles and an air-orifice, and a spinning process. According to these publications, it has been regarded as possible to produce microfine fibers according to a side-by-side type conjugate, melt-blow spinning process, even in combinations of herterogeneous polymers such as polyester/polypropylene, nylon 6/polypropylene, etc. as conjugate components.
In the spinneret device and the production process of conjugate fibers disclosed in the above two publications, it has been regarded that viscosities of heterogeneous polymers passing through the die should be generally similar, and can be achieved by controlling the temperature and retention time inside the extruder, the composition of the polymer, etc. Namely, in the production process, only when the heterogeneous polymers reach the spinning nozzles in a state where the respective extrusion temperatures and retention times have been controlled so that the respective viscosities have become almost equal, and also when they flow through the inside of the spinneret while retaining the balance between the respective viscosities, the polymers can form a conjugate mass which is then extruded through nozzles of the spinneret without any notable turbulence or break at the conjugate portions to form conjugate blow fibers. However, according to such a spinneret device, it is possible to obtain uniform conjugate melt-blown fibers only when the temperature and retention time inside the extruder and the composition of the polymers, etc. are controlled precisely while employing a relatively small spinneret having a short retention time, without taking productivity into consideration.
Namely, when a commercial spinneret device is taken into consideration, the following problems occur. When a viscosity difference has occurred between the respective melted polymers due to the variation in the molecular weights of the polymers themselves, accompanied by a slight variation in the extrusion temperatures, then turbulence of flow of the polymers melted inside the spinneret device occurs, making it impossible to obtain a uniform conjugate mass inside the cavity of the spinneret device. Hence it is impossible to form uniform, conjugate blow fibers.
Further, even if the temperature inside the extruder has been precisely controlled so as to maintain the viscosities of the polymers at definite values, when a large spinneret is used for productivity, polymers having different fluidities flow through the spinneret kept at the same temperature, so that the retention time inside the spinneret device is prolonged and hence the viscosity balance is broken due to the difference of fluidities of the polymers making it impossible to form uniform, conjugate blown fibers, and the uneven fineness of the resulting fibers increases.
Japanese patent application laid-open No. Hei 2-289107 disclosed a side-by-side type, conjugate, melt-blow spinneret device provided with a slender groove-form, confluent resin flow-controlling part having a defined ratio of length to thickness in the length direction of the spinneret, engraved at the bottom part of the nozzle plate 5 in the length direction, nozzle plate 5 having spinning holes 15 engraved at the above bottom part, and separating plates 4 for separating two kinds of melted resins, provided in the cavity of the device (see FIGS. 17 and 18). Further, the above publication also discloses a spinneret having a circular pipe part 25 for inserting a mixer into the bottom of the confluent resin flow-controlling part 23 (see FIG. 19). According to the device, the engraved, confluent resin flow-controlling part has the defined ratio of length to thickness in the length direction of the spinneret; therefore, even when spinning melted resins having viscosities that are somewhat different from each other are used as the first component and the second component of the conjugate fibers, the conjugate ratio, the fineness consistency, etc. are somewhat improved, as compared with the prior art of the above publications, but since any mechanism for a uniform confluence of conjugate components and for a uniform distribution of these components corresponding to the respective spinning nozzles are not provided, the above-mentioned problems have not yet been solved.
As described above, in any of the above prior art, no consideration has been taken about a uniform confluence mechanism and a uniform distribution mechanism of conjugate components directed to all of the individual spinning nozzles.